In one aspect, this invention relates to laser apparatus in which multiple laser cavities are contained within a unitary housing. The laser cavities may all be of the same type, power and wavelengths or they may be of different power levels, wavelengths and types. One such laser apparatus is sold under the trademark VersaPulse by Lumenis of Yokneam, Israel. In the apparatus, four laser cavities are contained in a unitary housing. The outputs of the four laser cavities may be combined by using suitable mirrors and lenses so that the output is a single laser beam which is the combined output of the four laser cavities. In the device, a 90 degree step-rotating mirror folds and combines the four beams sequentially from the four laser cavities into a common optical path. The device is also described generally in the following US patents, all of which are herein incorporated in their entirety by reference: U.S. Pat. Nos. 5,375,132, 5,659,563, 5,781,574, 5,999,555 and 6.115.396. Of course, depending on the number of laser cavities and the housing in which the laser cavities are installed, the 90 degree rotating mirror may be a lesser or a greater number of degrees. In this type device, the 90 degree step-rotating mirror optically switches the laser outputs from the four cavities. The relative position of the step-rotating mirror relative to each laser cavity defines the overlap-level of the laser beams along their common optical path. Ideally, all four laser beams are fully aligned into a single and uniform common optical path without any offsets. However, since the step-rotating mirror is limited to 90 degrees steps only and since the position of the four cavities is not precisely in exact 90 degrees orientation to each other (for example, 90+/−0.5 degrees), aligning the step-rotating mirror to one cavity results in some misalignment to the others. The above degree of uncertainty is the primary reason of mutual misalignment of the four laser cavities.
The lasers are fired rapidly, the mirror must react and be able, as it rotates in steps, to combine all the beams so that a uniform, fully overlapped single beam is outputted from the apparatus. The four laser beams are separated in time due to the rotating mirror but the optical path must be the same and aligned. In the above known device, prior to the present invention, the alignment point of the step-rotating mirror actually averages the four optimal alignment points of each of the four cavities. However, this may lead to a reduction in the overall combined laser beam output quality as a result of four slightly different optical paths
Turning now to FIG. 1, the figure shows a schematic of a multiple laser cavity apparatus. Although only two laser cavities are shown, this is due to the perspective of the drawing. It can be seen that in a perspective orthogonal to the page that two additional laser cavities can be accommodated. As can be seen in FIG. 1, the laser cavities 10 and 12 output two laser beams to an arrangement whereby each impinges on mirrors 14, 16, 18 and 20. Those mirrors then reflect the respective laser beam onto a rotating mirror 22 which is driven by a servo motor and position encoder 24. It is to the rotating mirror and position encoder that the present invention is, in part, directed. The rotating mirror, as can be seen in FIG. 1, then directs the two light beams b 26 and 28 from, respectively, laser cavities 12 and 10 onto first and second mirrors 30 and 32 and eventually to output 34. The third and fourth cavities have similar optical paths like 10 and 12 and they also combine in the rotating mirror 30. Mirrors 30 and 32 are common for the four laser beams from the four laser cavities. The beams are separated in time not slightly. They are sequentially generated by the four laser cavities. The rotating mirror needs to arrive at the right position at the right time to reflect the appropriate beam along the same optical path. If not so, the optical paths will differ from one another. A safety shutter 36 is also included the light path as seen in FIG. 1, the purpose of which will be discussed in greater detail below. Changes made to the structure and operation of the servo motor mirror the servo motor and position encoder will be described below in the section entitled “Detailed Description” below.
In another aspect, apparatus such as described above which includes multiple laser cavities or even a singular laser cavity require a source of power to charge the flash lamps such as 40 and 42. Conventionally, in known devices this may be accomplished by charging one or more large capacitors in a capacitor bank and rapidly discharging those capacitors into the flash lamps thus causing excitation of the laser rods 44 and 46 as seen in FIG. 1. Existing systems and off-the-shelf lamp switches and IGBTs function well to “fast charge” these capacitor banks. This provides the ability to quickly charge already discharged capacitors from a low-energy state to a high energy state at a fast rate. However, there is no off-the-shelf, easy solution to discharge. In normal practice, the preference is to discharge the full energy from the capacitors and not to stop at some point in the discharge process. Power levels may range from 20-150 watts or from 100-150 watts.
However, in many applications, it may be desirable for the operator of a laser apparatus such as, but not limited to, the above described apparatus to change the pulse width from among: a short pulse, a medium pulse and a long pulse. One aspect of the present invention is directed to a solution to allow rapid and controlled discharge of the capacitor banks so that the pulse width may be rapidly changed and controlled by the user through the user interface. A full explanation of the operation and structure of this aspect of the present invention will be found in the “Detailed Description” below.
In yet another aspect, in known laser apparatus devices the laser cavities are cooled, usually by water. Allowing the laser to become too hot can cause overheating, faulty operation, decreasing laser efficiency and even destruction of the laser cavity, all undesirable results. In addition, it is desirable that the laser apparatus operate in a normal ambient room temperature and humid environment rather than a specialized, climate-controlled environment. A specialized environment required a sealed and controlled environment. It is another aspect of the present invention to create a laser system which is not sealed and in fluid communication with the ambient room environment. In known systems having laser cavities which are open to ambient room conditions, the water which is used to cool the laser cavities and the remainder of the laser apparatus is not actively cooled to avoid condensation. Ambient room temperature systems, having a volume of water large enough to absorb the heat from the laser and through known heat exchange devices and this is usually sufficient to keep the laser at normal operating temperature. In contrast, sealed laser cavities may actively cool the water without risking damage to the cavity due to condensation. Laser energy absorption by condensed water, especially condensed water on the laser rod and especially on the lasing side of the rod, may significantly harm the laser cavity. This is risk which is greatly increased with solid state lasers having high absorption coefficients in water such as Holmium and the like having wavelengths higher than about 1.5 microns. However, in order to operate, open cavity lasers such as in accordance to one aspect of the present invention in other than ideal ambient temperature situations including high humidity situations, present non-active cooling systems may be insufficient to keep laser cavities at an ideal temperature in which they operate most efficiently and potentially cause damage and/or destruction to the laser cavities due to overheating. The main reason why this is not desirable is the decreased in the output power due to the apparatus having to work at higher temperatures. Thus, there is a need for a more efficient, active cooling system to allow for cooling of the lasers in both ideal and not so ideal environments in an open cavity configuration. This aspect of the present invention is further described in the “Detailed Description” below.
In yet another aspect, one application of the above described laser apparatus is, by way of example only, applying the output of the combined laser beams in the apparatus of the present invention to break up kidney stones or stones in the bladder. Typically, this is done by outputting the laser beam 34 of FIG. 1 through to a suitable optical fiber which is threaded into the kidneys and or the bladder. The laser output beam travels from the output 34 through the optical fiber and exits at an optical fiber end within the bladder or kidney and is aimed, for example, at the stones to break them up. An aiming beam may also be present to allow the physician to accurately aim the ablation laser at the desired target to be fragmented. Typically, the aiming beam may be a 532 nm green aiming beam and the ablation beam may be a Holmium beam of 2100-2112 nm. Also, there may be a need to provide an apparatus which may allow fast switching of the output laser state from a high energy cutting/ablation state to a lower energy, coagulating state.
It is to the above aspects of the present invention that the below “Detailed Description” is directed.